CN1328421A - Apparatus and method for improving hydrate formation and expansion agent recovery efficiency during expansion of tobacco leaves and other agricultural products - Google Patents

Abstract

An apparatus and method for recovering additional expansion agent during the expansion of tobacco or other agricultural products is disclosed. One embodiment is a method of recovering additional expansion agent during expansion of tobacco or other agricultural products, the method having a multi-step depressurization sequence including at least first and second depressurization steps for depressurizing an impregnation vessel, the method including the steps of withdrawing substantially all of the quantity of expansion agent in the impregnation vessel during the multi-step depressurization sequence at about the end of the second depressurization step, and feeding at least a portion of said quantity of expansion agent to a low pressure gas storage tank. In one embodiment, the expansion agent is carbon dioxide.

Description

Apparatus and method for improving hydrate formation and expansion agent recovery efficiency during expansion of tobacco leaves and other agricultural products

The present invention relates to a method of puffing agricultural products, such as tobacco leaves, food or other similar products, by impregnating the product with an expanding agent under the conditions of high pressure and saturation temperature of the expanding agent, and then subjecting the impregnated product to conditions that promote the expansion of the expanding agent. Substance methods and systems. In particular, the present invention relates to a method and apparatus for recovering additional quantities of carbon dioxide or other similar expansion agents in such processes or systems, which method and apparatus enable improved hydrate formation and improved recovery of carbon dioxide or other similar expansion agents. recycling efficiency.

As discussed in US Patent No. 5,143,096 (Steinberg), a number of methods are known for expanding porous materials including tobacco leaves and other agricultural products. Generally, these methods involve introducing an expanding agent, ie, an expanding substance capable of undergoing a phase transition, eg, from a liquid to a gas, into the pores of the substance and expanding the expanding agent.

It is also known to expand the porous mass by impregnating the porous mass with a liquefied gas expansion agent such as liquefied carbon dioxide under high pressure; curing; and heating the porous mass, such as by exposure to a hot gas stream, eg, steam, air, etc., to evaporate or sublime the cured expansion agent. The solidified expansion agent evaporates at a rate greater than the rate at which the expansion agent in gaseous form would be able to escape from the porous mass. The result of this treatment is that the substance is forced to expand.

The use of carbon dioxide as an expanding agent for puffing tobacco leaves is discussed, inter alia, in U.S. Patent Nos. 4,235,250 (Utsch); 4,258,729 (de la Burde et al); and 4,336,814 (Sykes et al). In the methods disclosed in these patents, carbon dioxide, in gaseous or liquid form, is brought into contact with tobacco leaves for impregnation, and the impregnated leaves are then subjected to rapid heat treatment to volatilize the carbon dioxide, thereby expanding the leaves.

U.S. Patent No. 4,340,073 (de la Burde et al.) discloses a method and apparatus for puffing tobacco leaves by impregnating the leaves with carbon dioxide under conditions, such as contacting the leaves with carbon dioxide in liquid form, to remove excess carbon dioxide from the leaves. Liquefying the carbon dioxide, reducing the pressure of the impregnated leaf to solidify the carbon dioxide within the leaf structure, and rapidly heating the leaf at atmospheric pressure to vaporize the carbon dioxide and expand the leaf.

British Patent Specification 1,484,536 (Michals) discloses a method of expanding organic matter, such as tobacco leaves, using liquid carbon dioxide. The method comprises the steps of pressurizing a vessel containing a substance to be expanded with carbon dioxide to a pressure in the range of approximately 200-1,070 psi, and immersing the substance in liquid carbon dioxide while the interior of the vessel maintains this pressure, thereby using carbon dioxide impregnation of the substance, removal of excess liquid carbon dioxide from the impregnation vessel, depressurization of the vessel to substantially atmospheric pressure, thereby solidifying the liquefied carbon dioxide on the surface and in the substance of the substance, removal of the impregnation from the vessel heated substance to expand the substance by at least 10%. In this method, the carbon dioxide used to pressurize the impregnation vessel is taken from the vapor space of the process vessel which supplies liquid carbon dioxide to the impregnation chamber. After removal of liquid carbon dioxide from the impregnation chamber, the carbon dioxide residual gas in the impregnation chamber is vented to the atmosphere or to a carbon dioxide recovery system (not shown in this patent specification).

Various recovery systems for carbon dioxide and other expansion agents, such as propane, used in tobacco leaf expansion methods disclosed in the prior art are described below.

US Patent No. 4,165,618 (Tyree, Jr.) discloses a method of treating a product such as tobacco leaf using a liquid refrigerant such as liquefied carbon dioxide. In this method, a vessel for impregnating tobacco leaves is purged and pressurized by introducing gas from the vapor space of a liquid refrigerant storage tank into the impregnating vessel. After pressurization, liquid refrigerant is introduced from the liquid storage tank into the impregnation vessel. The tobacco leaves are drawn into the liquid refrigerant for a predetermined period of time, after which the liquid refrigerant is returned to the liquid storage tank. The gaseous cryogen remaining in the impregnation vessel after liquid cryogen removal is then sent to a series of collectors where the gas is compressed and eventually returned to the liquid cryogen main storage tank.

US Patent No. 5,365,950 (Yoshimoto et al.) discloses an apparatus for puffing tobacco leaves using carbon dioxide as an expanding agent and regenerating the carbon dioxide using a pressure swing adsorption (PSA) device. The PSA unit is used as a recovery/separation unit to separate air (a dopant gas) from recovered carbon dioxide. The carbon dioxide is then compressed to a higher pressure and directed into the impregnation vessel. Several alternative embodiments are described utilizing one or more compressors to increase the pressure of recovered carbon dioxide.

U.S. Patent No. 5,311,885 (Yoshimoto et al.) discloses another apparatus for expanding tobacco leaves using carbon dioxide as an expansion agent and regenerating carbon dioxide using a PSA device for carbon dioxide recovery/separation, which is similar to U.S. Patent No. 5,365,950.

US Patent No. 5,711,319 (Cumner) discloses a method of leaf expansion using carbon dioxide. The carbon dioxide gas discharged from the impregnation vessel during the depressurization step is collected in the carbon dioxide recovery spherical tank. The gas in the recovery sphere is recompressed with a compressor and reliquefied with a heat exchanger before being returned to a process vessel. The CO2 storage tank is recharged with CO2 gas directly from the compressor. Alternatively, the carbon dioxide gas vented from the impregnation vessel during the depressurization step is collected in an intermediate pressure vessel maintaining part of the vented gas pressure, and the remainder is vented into a recovery spherical tank. Preferably, one compressor is provided to send the gas from the recovery sphere to the intermediate pressure vessel, and a second compressor is used to send the gas to the heat exchanger. The reliquefied carbon dioxide from the heat exchanger is then returned to the process tank. Gas replenishment to the carbon dioxide containing storage tank is obtained directly from the second compressor.

US Patent No. 5,819,754 (Conrad et al.) discloses an apparatus and method for expanding tobacco leaves with an expanding agent such as propane. After a predetermined impregnation period, some bulking agent is released from the impregnation zone into the regeneration collector (the propane returned to the collector is regenerated and used in subsequent leaf treatment cycles). An expander recovery line is provided to further remove propane remaining in the impregnation zone and not being regenerated due to pressure equalization in the collector and chamber. It also provides for periodic removal of the high pressure expansion agent from the impregnation zone so that contaminants (eg, moisture, etc.) do not build up to undesired levels in the expansion agent. In order to recover expansion agent or recover energy therefrom, the expansion agent recovery line is connected to a preferred gas recovery or disposal zone (not shown in the patent).

Tobacco leaf puffing devices can generally be divided into batch type puffing devices and continuous type puffing devices. In a typical batch-type expansion unit, a predetermined amount of tobacco leaf material is stored in an impregnation vessel, high-pressure carbon dioxide is introduced into the impregnation vessel to impregnate the tobacco leaf material with carbon dioxide, and the tobacco leaf material is then removed to expand the tobacco leaf material. In a continuous expansion unit, tobacco leaf material and carbon dioxide are continuously introduced into an impregnation vessel.

Although the batch type device has a simple structure, its efficiency is low and a large amount of carbon dioxide is lost. More recently designed continuous type extruders have higher efficiencies and are capable of recovering and reusing carbon dioxide as shown in the above discussed patents US Nos. 5,311,885 and 5,365,950 to Yoshimoto et al.

Many traditional methods, including the Dry Ice Expanded Tobacco (DIET) method and other CO2 expansion methods, do not recycle and reuse all available expansion agents (such as CO2), some are vented to the atmosphere, in addition to increasing emissions to the environment In addition to emissions, this results in less than ideal performance of the process in terms of efficiency and economy.

It would be desirable to have an improved method and system for expansion of agricultural products, such as tobacco leaves, food products, or other similar substances, which overcomes the disadvantages of the prior art.

It would further be desirable to have a more efficient and economical method and system for the expansion of agricultural products, such as tobacco leaves, food products, or other similar substances.

It is further desired to have an improved method and system for expanding agricultural products, such as tobacco leaves, food products, or other similar substances, using carbon dioxide as the expansion agent.

It is further desirable to have an improved method and system for extruding agricultural products, such as tobacco leaves, food products, or other similar substances, and in such method and system for recovering additional amounts of carbon dioxide, or in the method and system Another similar expansion agent.

It is still further desired to have an improved method and system for expanding agricultural products, such as tobacco leaves, food products, or other similar substances, with improved hydrate generating means for better expansion and more uniform expansion of such products.

The present invention is a method and device for recovering additional expansion agent in the expansion process of tobacco leaves or other agricultural products, such as food or other porous products. The present invention includes a method for the expansion of tobacco leaves or other agricultural products, wherein the method includes a method of recovering additional expansion agent. The invention also includes an expanded tobacco leaf product or other product produced according to the method. Additionally, the present invention includes a system for expansion of tobacco leaves or other agricultural products, wherein the system includes a means for recovering additional expansion agent.

A first embodiment of the present invention is a method of recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization comprising at least first and second depressurization steps of depressurizing the impregnation vessel A procedure comprising the steps of: withdrawing all of the quantity of expansion agent in the impregnation vessel at approximately the end of the second depressurization step during the multi-step depressurization procedure; sending at least a portion of said quantity of expansion agent into a low-pressure gas storage tank .

A second embodiment of the present invention is a method of recovering additional expansion agent comprising the additional steps of: withdrawing at least a portion of the expansion agent from the low-pressure gas storage tank; compressing the expansion agent extracted from the low-pressure gas storage tank; compressing the compressed feeding the expansion agent into the high-pressure gas storage tank; withdrawing at least a portion of the compressed expansion agent from the high-pressure gas storage tank; further compressing the compressed expansion agent drawn from the high-pressure gas storage tank; condensing the further compressed expansion agent; Store the condensed expansion agent in the container.

A third embodiment is a method of recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps for depressurizing the impregnation vessel , comprising the steps of: during the multi-step decompression process, at about the end of the second depressurization step, withdrawing substantially all of the amount of expansion agent in the impregnation vessel; and compressing at least a portion of said amount of expansion agent to a sufficient pressure to condense the expansion agent.

The fourth embodiment has two steps in addition to the steps in the third embodiment. An additional step is to condense the compressed expansion agent and store the condensed expansion agent in a storage tank.

The fifth embodiment has one step in addition to the step in the fourth embodiment. An additional step is to regulate the mass flow of said quantity of bulking agent drawn from the impregnation vessel at a sufficient mass flow rate for maximum hydration of the bulk water in the tobacco leaves or other agricultural products.

A sixth embodiment is a method of recovering additional swelling agent as in the third embodiment, but comprising the additional step of: during the reduced pressure range from the initial impregnation pressure to the pressure at which the swelling agent ceases to hydrate, Determine the most appropriate depressurized mass flow rate for maximum hydrate formation. In a variant embodiment, this additional step comprises the following steps: (a) setting the mass flow rate of the expansion agent at the selected mass flow rate; (b) at approximately the end of the impregnation cycle, determining (c) adjust the mass flow rate of the bulking agent by an increment; and (d) repeat steps (b), (c) and (d) until there is The maximum amount of bulking agent in the processed product is determined.

A seventh embodiment of the present invention is a method of expanding tobacco leaves or other agricultural products, wherein the method includes a method of recovering additional expansion agent as in the first embodiment.

An eighth embodiment is a method of expanding tobacco leaves or other agricultural products, wherein the method includes a method of recovering additional expansion agent as in the third embodiment.

A ninth embodiment is an apparatus for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing the impregnation vessel, which comprising: during the multi-step depressurization process, at about the end of the second depressurization step, means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel; and feeding at least a portion of said amount of expansion agent into a low-pressure gas storage Tank equipment.

The tenth embodiment of the present invention is a device for recovering additional expansion agent as in the ninth embodiment, but it includes the following additional equipment: equipment for extracting at least a part of the expansion agent from the low-pressure gas storage tank; Apparatus for extracting expansion agent; apparatus for feeding compressed expansion agent into high-pressure gas storage tanks; equipment for withdrawing at least a part of compressed expansion agent from high-pressure gas storage tanks; further compressing compressed expansion agent from high-pressure gas storage tanks means for condensing the further compressed expansion agent; and means for storing the condensed expansion agent in storage tanks.

An eleventh embodiment is an apparatus for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing the impregnation vessel, It comprises: during the multi-step depressurization process, at about the end of the second depressurization step, means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel; and compressing at least a portion of said amount of expansion agent to a sufficient pressure to condense the expansion agent.

The twelfth embodiment is an apparatus for recovering additional expansion agent as in the eleventh embodiment, but it includes the following additional equipment: equipment for condensing the compressed expansion agent; and equipment for storing the condensed expansion agent in a storage tank .

A thirteenth embodiment of the present invention is an apparatus for recovering additional bulking agent as in the eleventh embodiment, but which includes the following additional equipment: For maximum hydration of large amounts of water in tobacco leaves or other agricultural products, Means for regulating the mass flow of said quantity of expansion agent withdrawn from the impregnation vessel at a sufficient mass flow rate.

The fourteenth embodiment is an apparatus for recovering additional expansion agent as in the eleventh embodiment, but which includes the following additional equipment: a reduced pressure range for the initial impregnation pressure to the pressure at which the expansion agent ceases to hydrate During this period, determine the most suitable decompression mass flow rate equipment for maximum hydrate formation.

A fifteenth embodiment of the present invention is an expansion system for tobacco leaves or other agricultural products, wherein the system includes a device for recovering additional expansion agent as in the ninth embodiment.

A sixteenth embodiment of the present invention is an expansion system for tobacco leaves or other agricultural products, wherein the system includes a device for recovering additional expansion agent as in the eleventh embodiment.

A seventeenth embodiment of the present invention is an apparatus as in the thirteenth embodiment, wherein the regulating means comprises: a conduit adapted to convey the mass flow of said quantity of expansion agent withdrawn from the impregnation vessel to the compressing means a flow regulating valve connected; a differential flow measuring device connected to the flow regulating valve and the compression device; and a set point regulator connected to the flow regulating valve and the differential flow measuring device.

Another aspect of the invention is an expanded tobacco leaf product or other product produced according to the method of the seventh embodiment.

A further aspect of the invention is an expanded tobacco leaf product or other product produced according to the method of the eighth embodiment.

In any of the embodiments and aspects of the invention discussed above, the expansion agent may be carbon dioxide ( _CO2 ). However, expansion agents other than carbon dioxide may also be used, including but not limited to the list of expansion agents set forth in the detailed description of the invention and the appended claims.

For a better understanding of the invention, reference is made to the accompanying drawings. The drawings show several preferred embodiments of the invention. It should be understood, however, that the invention is not limited to the arrangements and methodologies shown in the drawings.

Fig. 1 represents in the production of expanded tobacco leaf, the process flow diagram diagram of the traditional carbon dioxide recovery method used;

Figure 2 shows a simplified process flow diagram of a carbon dioxide recovery method according to an embodiment of the invention used in the production of expanded tobacco leaves; and

Figure 3 shows a simplified process flow diagram of another embodiment of the present invention for carbon dioxide recovery process used in the production of expanded tobacco leaf.

Several embodiments of the invention are discussed herein with respect to methods of producing expanded tobacco leaves using carbon dioxide ( _CO2 ) as the expanding agent. However, the present invention is not limited to expanded tobacco leaf, but is also applicable to other expanded porous products and/or agricultural products, including but not limited to other methods and systems of food production. At the same time, in the present invention, other expansion agents can also be used instead of carbon dioxide, including but not limited to the following substances: ethylene (C ₂ H ₂ ), propylene (C ₃ H ₆ ), cyclopropane (C ₃ H ₆ ), propane (C ₃ H ₈ ), Isobutane (C ₄ H ₁₀ ), Chlorine (Cl ₂ ), Hydrogen Sulfide (H ₂ S), Nitrogen (N ₂ ), Oxygen (O ₂ ), Methane (CH ₄ ), Acetylene (C ₂ H ₂ ), ethane (C ₂ H ₆ ), methyl iodide (CH ₃ I), argon (A), arsine (AsH ₃ ), bromine (Br ₂ ), bromine chloride (BrCl), di Chlorine oxide (ClO ₂ ), dihydrogen selenide (H ₂ Se), krypton (Kr), methyl mercaptan (CH ₃ HS), nitrous oxide (N ₂ O), phosphine (PH ₃ ), sulfur dioxide (SO ₂ ), sulfur hexafluoride (SF ₆ ), sulfuryl chloride (SO ₂ Cl ₂ ), antimony hydrogen (SbH ₃ ), and xenon (Xe).

In addition, in the present invention, refrigerants can be used as expansion agents, including but not limited to the following substances: F-11 (CCl ₃ F), F-12 (CCl ₂ F ₂ ), F-12B1 (CClF ₂ Br ), F-13B1(CBrF ₃ ), F-20(CHCl ₃ ), F-21(CHCl ₂ F), F-22(CHClF ₂ ), F-30(CH ₂ Cl ₂ ), F-31(CH ₂ ClF), F-32(CH ₂ F ₂ ), F-40(CH ₃ Cl), F-40B1(CH ₃ Br), F-142b(CH ₃ CCIF ₂ ), F-152a(CH ₃ CHF ₂ ), F-12B2(CF ₂ Br ₂ ), F-22B1(CHBrF ₂ ), F-41(CH ₃ F), F-150a(CH ₃ CHCl ₂ ), F-160(C ₂ H ₅ Cl), F-160B1 ( _C2H5Br ), _F -161 ( _C2H5F ) and F-1140 ( _CH2 = _CHCl ).

In this carbon dioxide expansion method, the production of expanded tobacco leaves utilizes carbon dioxide (CO ₂ ) as the expansion or impregnating agent. When this impregnating agent is placed in contact with tobacco leaves under appropriate temperature and pressure conditions, a bulking agent (such as CO ₂ hydrate) is formed in the tobacco leaves (note that "CO ₂ hydrate" is referred to as "bulking agent "(expanding agent), and CO ₂ is the "expansion agent" (expansion agent), sometimes called "impregnating agent"). When the impregnated tobacco leaves are subjected to rapid heating, the puffing agent decomposes, releasing a large amount of gas that expands the micropores of the tobacco leaves.

Figure 1 shows a conventional carbon dioxide recovery process and apparatus 10 for a carbon dioxide expansion process. Due to the physical properties of carbon dioxide, the contacting of the tobacco leaves with liquid carbon dioxide must take place in the impregnation vessel 12 under high pressure conditions. After a sufficient contact time, the liquid carbon dioxide in the impregnation vessel is vented and the impregnation vessel is depressurized.

The decompression method is usually performed in three steps (although a two-step method is acceptable, more often a three-step method is used). Referring to FIG. 1 , the decompression process includes a first decompression step of expanding carbon dioxide gas and flowing into a high-pressure gas storage tank 14 , followed by a second decompression step of flowing into a low-pressure gas storage tank 16 . In the third depressurization step, the carbon dioxide in the impregnation vessel 12 is vented to the atmosphere via the valve 18 . As a result of the third depressurization step, any available residual carbon dioxide present in the impregnation vessel is lost at the completion of the second depressurization step.

In order to recover the carbon dioxide produced in the first and second decompression steps and present in the high-pressure gas storage tank 14 and the low-pressure gas storage tank 16, the carbon dioxide gas is compressed to a sufficient pressure, condensed and stored under this pressure, for subsequent It is reused in a high pressure liquid storage tank 20 (not shown), as shown in FIG. 1 . To compress the carbon dioxide gas to condensing pressure, low pressure gas is pumped from low pressure gas storage tank 16 to high pressure gas storage tank 14 via valves 15 and 17 by low pressure gas compressor 22 . High pressure gas is pumped by high pressure gas compressor 24 from high pressure gas storage tank 14 to a condenser (not shown) through valves 19 and 21 . After condensation, the recovered liquid is stored in a high pressure liquid storage tank 20 (not shown).

By improving the decompression method and equipment of the prior art, according to the first preferred embodiment of the present invention, as shown in Figure 2, during the third decompression step process, the gas that is normally discharged into the atmosphere (in the traditional method of Figure 1) Carbon dioxide can instead be recovered for reuse. This recovery of additional carbon dioxide results in lower production costs and reduces emissions into the atmosphere.

The carbon dioxide recovery process 30 shown in FIG. 2 utilizes the low pressure gas compressor 22 to depressurize the impregnation vessel 12 from the end of the second depressurization step by pumping available surplus carbon dioxide directly from the impregnation vessel to the low pressure gas storage tank 16. The pressure at that time was decompressed to atmospheric pressure. This is achieved by the installation of a valve 23 and a line 29 directly connecting the impregnation vessel 12 to the suction side of the low pressure gas compressor 22 . Low pressure gas compressor 22 pumps carbon dioxide from impregnation vessel 12 to low pressure gas storage tank 16 via valve 25 and line 31 . When the impregnation vessel has reached atmospheric pressure, the vessel is opened, the product discharged, and the process of producing expanded tobacco leaves continued. The additional recovered carbon dioxide present in the low pressure gas storage tank 16 at this time is compressed and recovered in the normal procedure described above (for the prior art method shown in Figure 1). This improved depressurization and carbon dioxide recovery method as shown in Figure 2 can be carried out in any existing plant for expanding tobacco leaves.

In the impregnation vessel 12, the tobacco leaves are immersed in liquid carbon dioxide at a pressure between 29 and 32 bar gauge to saturate the pores of the tobacco leaves. The excess carbon dioxide is then drained from the impregnation vessel, leaving only the liquid carbon dioxide absorbed in the tobacco leaves and the surrounding equilibrium gas. In order to generate the puffing agent, ie CO ₂ hydrate, in the tobacco leaves, it is necessary that the carbon dioxide molecules and water molecules (in the tobacco leaves) are cooled to produce the puffing agent. (As noted earlier, " _CO2 hydrate" is known as an "expanding agent", while _CO2 is an "expansion agent", sometimes called an "impregnating agent".)

The chemical formula of CO ₂ hydrate is CO ₂ ·6H ₂ O, and the chemical equation ←+heat CO ₂ +6H ₂ O is used to balance CO ₂ ·6H ₂ O-heat→ to represent the reversible reaction of hydrate formation. In the prior art of the carbon dioxide expansion process, the cooling required to form hydrates is achieved by depressurizing the impregnation vessel 12 to a high-pressure gas storage tank 14 and a low-pressure gas storage tank 16 in a two-step process, terminating below the carbon dioxide three-phase This is achieved by evaporating part of the liquid carbon dioxide absorbed in the tobacco leaves in the pressure well of the point (4.17 bar gauge pressure). If sufficient water is available in the leaf (normally about 20% by wet weight), and if the evaporation rate of liquid carbon dioxide is sufficient to remove the heat of hydration from the leaf/water/CO _matrix , Hydrates can be formed during the whole process of reducing the initial impregnation pressure to below the triple point of carbon dioxide. Hydrates are formed at temperatures slightly above (3-7°C) the freezing point of water at the same salinity. The hydrate formation reaction is exothermic, and the heat of hydrate (131.5 cal/gm water hydration) requires much more cooling than the freezing of water (80 cal/gm water freezes) to effectuate the reaction. If the cooling rate drops below the heat of hydration due to the evaporation of liquid carbon dioxide, some of the water will freeze and will no longer be available for hydration.

In the two-step decompression of the carbon dioxide expansion method, when the valve 26 from the immersion vessel 12 to the high-pressure gas storage tank 14 is opened (see FIG. 1 ), the evaporation rate of liquid carbon dioxide is very high. When the pressure differential between the tanks 14 is very high, sufficient cooling is produced to induce good hydration. As the pressure in the impregnation vessel decreases and the pressure in the high pressure gas storage tank increases, due to flow towards the equilibrium pressure between the two vessels, the pressure differential reaches a point where the evaporation rate of carbon dioxide is too low to form hydrates , but still well above the point where water freezes to ice. When pressure equilibrium is reached between the two vessels, the second step of depressurization begins. Likewise, when the impregnation vessel 12 is discharged into the low pressure gas storage tank 16, hydration occurs, evaporation is reduced, water-ice is formed, and the remaining carbon dioxide becomes dry ice at the triple point of carbon dioxide. The gas in the impregnation vessel can be recovered or vented via valve 18 to atmosphere.

Using tobacco leaves at 20% humidity in the impregnation vessel 12, if all available water is hydrated, the theoretical maximum hydrate formation can be as high as 8.7% of the _CO2 becomes hydrated, based on the wet weight of the tobacco leaves. Typical hydrate formation in this embodiment of the process is in the range of 2-3% of the _CO2 converted as hydrate. If the _CO2 becoming hydrated is below 2.0%, the expansion of the tobacco leaf is very poor, while the treatment unit is run at a level closer to 3% indicating better overall product quality.

A second preferred embodiment of the present invention is shown in FIG. 3 . This embodiment is suitable for existing process plants as well as new or future process plants, and for depressurization of the impregnation vessel 12, it is believed that the method provides more efficient recovery of carbon dioxide.

Referring to Figure 3, it can be noted that this embodiment 40 utilizes a compression system comprising a multi-stage or compound compressor 42 connected directly to the impregnation vessel 12 (those skilled in the art will recognize that a single-stage compressor in series Combination, like the combination of other compression equipment, can be used instead of multi-stage compressors). The compression system is capable of compressing carbon dioxide from atmospheric pressure to a pressure in storage tank 20 (not shown) equal to a pressure sufficient to condense the expansion agent (approximately 35.5 bar gauge for carbon dioxide). This solution eliminates the need for a high pressure gas storage tank 14 and a low pressure gas storage tank 16 . Connecting the compressor directly to the impregnation vessel does not preclude the installation of a separator vessel ("knockout pot") (not shown) between the impregnation vessel and the compressor. The separator vessel will remove any entrained tobacco fines from the air stream, if necessary.

Another important advantage of using a multi-stage or compound compressor 42 to depressurize the impregnation vessel 12, as shown in Figure 3, is the ability to adjust the pressure leaving the impregnation vessel 12 at any rate sufficient for maximum hydration of the water in the tobacco leaves. The mass flow rate of the gas in the container. This requires installation of a customary flow regulating valve 44 on the line 28 exiting the impregnation vessel and a conventional differential flow measuring device 46 between the regulating valve 44 and the suction line of the compound compressor 42 . The flow regulating valve and the differential flow measuring device are connected together in a regulating circuit using a conventional fixed value regulator 48 . Those skilled in the art will recognize that alternatives are possible in which the differential flow measurement device 46 can be installed upstream of the regulator valve 44 . Those skilled in the art will also recognize that during the entire reduced pressure range from the initial impregnation pressure to the pressure at which the expanding agent ceases to form hydrates (when the expanding agent is carbon dioxide, this pressure is the triple point of carbon dioxide), Determining the optimal decompression mass flow rate for maximum hydrate formation is easy.

An iterative method is used to determine the optimum reduced pressure mass flow by setting the mass flow rate of the bulking agent to a selected value and at the end of the steeping process, determining the amount of bulking agent present in the dipped product by laboratory analysis Rate. After making the determination, the mass flow rate of the expansion agent is adjusted incrementally, and the method is repeated. Subsequently, the adjustment of the bulking agent mass flow rate is carried out until the maximum amount of bulking agent present in the dipped product is found.

In embodiment 40, the elimination of high and low pressure gas storage tanks (14, 16) reduces the hardware cost of the overall system. A multi-stage or compound compressor can be designed to control three impregnation vessels as the maximum time the compressor will be used is about 300 seconds out of a total cycle time of about 1000 seconds.

While various embodiments of the present invention have been discussed above, it should be appreciated that various changes and modifications can be made to those embodiments without departing from the spirit and scope of the invention as defined by the appended claims.

Our invention has been sufficiently described and illustrated above that without further elaboration, the method can be readily adopted by others by applying present and/or future knowledge under various operating conditions.

Claims (24)

1. A method of recovering additional expansion agent during expansion of tobacco leaves or other agricultural products, the method having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing an impregnation vessel, comprising the steps of : During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and Sending at least a portion of said quantity of expansion agent into a low pressure gas storage tank. 2. A method of reclaiming extra expansion agent as claimed in claim 1, further comprising the steps of: withdrawing at least a portion of the expansion agent from the low-pressure gas storage tank; Compress the expansion agent drawn from the low-pressure gas storage tank; Send the compressed expansion agent into the high-pressure gas storage tank; withdrawing at least a portion of the compressed expansion agent from the high pressure gas storage tank; Further compressing the compressed expansion agent drawn from the high-pressure gas storage tank; condensing the further compressed expansion agent; and Store the condensed expansion agent in a storage tank. 3. A method of recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing the impregnation vessel, comprising the steps of : During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and Compressing at least a portion of said amount of expansion agent to a pressure sufficient to condense the expansion agent. 4. A method of reclaiming extra expansion agent as claimed in claim 3, further comprising the steps of: condensing compressed expansion agent; and Store the condensed expansion agent in a storage tank. 5. A method of reclaiming extra expansion agent as claimed in claim 3, further comprising the steps of: The mass flow of said quantity of bulking agent withdrawn from the impregnation vessel is adjusted at a sufficient mass flow rate for maximum hydration of the bulk water in the tobacco leaves or other agricultural products. 6. A method of reclaiming additional expansion agent as claimed in claim 3, further comprising the steps of: The most suitable depressurized mass flow rate for maximum hydrate formation is determined during the depressurized pressure range from the initial impregnation pressure to the pressure at which the expansion agent ceases to hydrate. 7. A method of expanding tobacco leaves or other agricultural products, wherein the method comprises a method of recovering additional expansion agent, the method having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing an impregnation vessel , which includes the following steps: During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and Sending at least a portion of said quantity of expansion agent into a low pressure gas storage tank. 8. A method of expanding tobacco leaves or other agricultural products, wherein the method comprises a method of recovering additional expansion agent, the method having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing an impregnation vessel , which includes the following steps: During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and Compressing at least a portion of said amount of expansion agent to a pressure sufficient to condense the expansion agent. 9. An apparatus for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing an impregnation vessel, comprising: During a multi-step depressurization process, at about the end of the second depressurization step, means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel; and Means for feeding at least a portion of said quantity of expansion agent into a low pressure gas storage tank. 10. A device for recovering additional expansion agent as claimed in claim 9, further comprising: Equipment for withdrawing at least a portion of the expansion agent from low-pressure gas storage tanks; Equipment for compressing expansion agent drawn from low-pressure gas storage tanks; Equipment for feeding compressed expansion agent into high-pressure gas storage tanks; Equipment for withdrawing at least a portion of the compressed expansion agent from high-pressure gas storage tanks; Equipment for further compressing the compressed expansion agent drawn from the high-pressure gas storage tank; equipment for condensing further compressed expansion agent; and A device for storing condensed expansion agent in a storage tank. 11. An apparatus for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having a multi-step depressurization process comprising at least first and second depressurization steps of depressurizing an impregnation vessel, comprising: During a multi-step depressurization process, at about the end of the second depressurization step, means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel; and means for compressing at least a portion of said quantity of expansion agent to a pressure sufficient to condense the expansion agent. 12. A device for recovering additional expansion agent as claimed in claim 11, further comprising: Equipment for condensing compressed expansion agent; and A device for storing condensed expansion agent in a storage tank. 13. A device for recovering additional expansion agent as claimed in claim 11, further comprising: Means for regulating the mass flow of said quantity of bulking agent withdrawn from the impregnation vessel at a sufficient mass flow rate for maximum hydration of large quantities of water in tobacco leaves or other agricultural products. 14. A device for recovering additional expansion agent as claimed in claim 11, further comprising: Apparatus for determining the most appropriate depressurized mass flow rate for maximum hydrate formation during the depressurized pressure range from the initial impregnation pressure to the pressure at which the expansion agent ceases to hydrate. 15. An expansion system for tobacco leaves or other agricultural products, wherein the system includes a means for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having at least first and second steps comprising depressurizing an impregnation vessel A multi-step decompression process of two decompression steps, which includes: means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel near the end of the second depressurization step during the multi-step depressurization process; and Means for feeding at least a portion of said quantity of expansion agent into a low pressure gas storage tank. 16. An expansion system for tobacco leaves or other agricultural products, wherein the system includes a means for recovering additional expansion agent during the expansion of tobacco leaves or other agricultural products, the process having at least first and second steps comprising depressurizing an impregnation vessel A multi-step decompression process of two decompression steps, which includes: means for withdrawing substantially all of the amount of expansion agent in the impregnation vessel near the end of the second depressurization step during the multi-step depressurization process; and means for compressing at least a portion of said quantity of expansion agent to a pressure sufficient to condense the expansion agent. 17. An apparatus as claimed in claim 13, wherein said adjustment means comprises: a flow regulating valve connected to a conduit suitable for conveying the mass flow of said quantity of expansion agent withdrawn from the impregnation vessel to the compression device; a differential flow measuring device connected to the flow regulating valve and the compression device; and A setpoint regulator connected to a flow regulating valve and a differential flow measuring device. 18. An expanded tobacco leaf product or other product produced according to a method of expansion of tobacco leaf or other agricultural product, wherein the method comprises a method of recovering additional expansion agent having at least first and second steps comprising depressurizing an impregnation vessel The multi-step decompression procedure of two decompression steps, it comprises the following steps: During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and Sending at least a portion of said quantity of expansion agent into a low pressure gas storage tank. 19. An expanded tobacco leaf product or other product produced according to a method of expansion of tobacco leaf or other agricultural product, wherein the method includes a method of recovering additional expansion agent, the method having at least first and second steps comprising depressurizing an impregnation vessel The multi-step decompression procedure of two decompression steps, it comprises the following steps: During the multi-step depressurization process, at about the end of the second depressurization step, substantially all of the amount of expansion agent in the impregnation vessel is withdrawn; and At least a portion of said amount of expansion agent is compressed to a pressure sufficient to condense the expansion agent. 20. A method as claimed in claim 1, wherein the expansion agent is selected from the group consisting of carbon dioxide (CO ₂ ), ethylene (C ₂ H ₂ ), propylene (C ₃ H ₆ ), cyclopropane (C ₃ H ₆ ), propane (C ₃ H ₈ ), isobutane (C ₄ H ₁₀ ), chlorine (Cl ₂ ), hydrogen sulfide (H ₂ S), nitrogen (N ₂ ), oxygen (O ₂ ), methane ( CH ₄ ), acetylene (C ₂ H ₂ ), ethane (C ₂ H ₆ ), methyl iodide (CH ₃ I), argon (A), arsine (AsH ₃ ), bromine (Br ₂ ), bromine chloride (BrCl), chlorine dioxide (ClO ₂ ), dihydrogen selenide (H ₂ Se), krypton (Kr), methyl mercaptan (CH ₃ HS), nitrous oxide (N ₂ O), phosphine ( PH ₃ ), sulfur dioxide (SO ₂ ), sulfur hexafluoride (SF ₆ ), sulfuryl chloride (SO ₂ Cl ₂ ), antimony hydrogen (SbH ₃ ), and xenon (Xe), F-11 (CCl ₃ F) , F-12(CCl ₂ F ₂ ), F-12B1(CClF ₂ Br), F-13B1(CBrF ₃ ), F-20(CHCl ₃ ), F-21(CHCl ₂ F), F-22(CHClF ₂ ), F-30(CH ₂ Cl ₂ ), F-31(CH ₂ ClF), F-32(CH ₂ F ₂ ), F-40(CH ₃ Cl), F-40B1(CH ₃ Br), F-142b(CH ₃ CCIF ₂ ), F-152a(CH ₃ CHF ₂ ), F-12B2(CF ₂ Br ₂ ), F-22B1(CHBrF ₂ ), F-41(CH ₃ F), F-150a (CH ₃ CHCl ₂ ), F-160 (C ₂ H ₅ Cl), F-160B1 (C ₂ H ₅ Br), F-161 (C ₂ H ₅ F) and F-1140 (CH ₂ =CHCl). 21. A method as claimed in claim 3, wherein the expansion agent is selected from the group consisting of carbon dioxide (CO ₂ ), ethylene (C ₂ H ₂ ), propylene (C ₃ H ₆ ), cyclopropane (C ₃ H ₆ ), propane (C ₃ H ₈ ), isobutane (C ₄ H ₁₀ ), chlorine (Cl ₂ ), hydrogen sulfide (H ₂ S), nitrogen (N ₂ ), oxygen (O ₂ ), methane ( CH ₄ ), acetylene (C ₂ H ₂ ), ethane (C ₂ H ₆ ), methyl iodide (CH ₃ I), argon (A), arsine (AsH ₃ ), bromine (Br ₂ ), bromine chloride (BrCl), chlorine dioxide (ClO ₂ ), dihydrogen selenide (H ₂ Se), krypton (Kr), methyl mercaptan (CH ₃ HS), nitrous oxide (N ₂ O), phosphine ( PH ₃ ), sulfur dioxide (SO ₂ ), sulfur hexafluoride (SF ₆ ), sulfuryl chloride (SO ₂ Cl ₂ ), antimony hydrogen (SbH ₃ ), and xenon (Xe), F-11 (CCl ₃ F) , F-12(CCl ₂ F ₂ ), F-12B1(CClF ₂ Br), F-13B1(CBrF ₃ ), F-20(CHCl ₃ ), F-21(CHCl ₂ F), F-22(CHClF ₂ ), F-30(CH ₂ Cl ₂ ), F-31(CH ₂ ClF), F-32(CH ₂ F ₂ ), F-40(CH ₃ Cl), F-40B1(CH ₃ Br), F-142b(CH ₃ CCIF ₂ ), F-152a(CH ₃ CHF ₂ ), F-12B2(CF ₂ Br ₂ ), F-22B1(CHBrF ₂ ), F-41(CH ₃ F), F-150a (CH ₃ CHCl ₂ ), F-160 (C ₂ H ₅ Cl), F-160B1 (C ₂ H ₅ Br), F-161 (C ₂ H ₅ F) and F-1140 (CH ₂ =CHCl). 22. A device as claimed in claim 9, wherein the expansion agent is selected from the group consisting of carbon dioxide (CO ₂ ), ethylene (C ₂ H ₂ ), propylene (C ₃ H ₆ ), cyclopropane (C ₃ H ₆ ), propane (C ₃ H ₈ ), isobutane (C ₄ H ₁₀ ), chlorine (Cl ₂ ), hydrogen sulfide (H ₂ S), nitrogen (N ₂ ), oxygen (O ₂ ), methane ( CH ₄ ), acetylene (C ₂ H ₂ ), ethane (C ₂ H ₆ ), methyl iodide (CH ₃ I), argon (A), arsine (AsH ₃ ), bromine (Br ₂ ), bromine chloride (BrCl), chlorine dioxide (ClO ₂ ), dihydrogen selenide (H ₂ Se), krypton (Kr), methyl mercaptan (CH ₃ HS), nitrous oxide (N ₂ O), phosphine ( PH ₃ ), sulfur dioxide (SO ₂ ), sulfur hexafluoride (SF ₆ ), sulfuryl chloride (SO ₂ Cl ₂ ), antimony hydrogen (SbH ₃ ), and xenon (Xe), F-11 (CCF), F -12(CCl ₂ F ₂ ), F-12B1(CClF ₂ Br), F-13B1(CBrF ₃ ), F-20(CHCl ₃ ), F-21(CHCl ₂ F), F-22(CHClF ₂ ) , F-30(CH ₂ Cl ₂ ), F-31(CH ₂ ClF), F-32(CH ₂ F ₂ ), F-40(CH ₃ Cl), F-40B1(CH ₃ Br), F- 142b(CH ₃ CCIF ₂ ), F-152a(CH ₃ CHF ₂ ), F-12B2(CF ₂ Br ₂ ), F-22B1(CHBrF ₂ ), F-41(CH ₃ F), F-150a(CH ₃ CHC), F-160 (C ₂ H ₅ Cl), F-160B1 (C ₂ H ₅ Br), F-161 (C ₂ H ₅ F) and F-1140 (CH ₂ =CHCl). 23. A device as claimed in claim 11, wherein the expansion agent is selected from the group consisting of carbon dioxide (CO ₂ ), ethylene (C ₂ H ₂ ), propylene (C ₃ H ₆ ), cyclopropane (C ₃ H ₆ ), propane (C ₃ H ₈ ), isobutane (C ₄ H ₁₀ ), chlorine (Cl ₂ ), hydrogen sulfide (H ₂ S), nitrogen (N ₂ ), oxygen (O ₂ ), methane ( CH ₄ ), acetylene (C ₂ H ₂ ), ethane (C ₂ H ₆ ), methyl iodide (CH ₃ I), argon (A), arsine (AsH ₃ ), bromine (Br ₂ ), bromine chloride (BrCl), chlorine dioxide (ClO ₂ ), dihydrogen selenide (H ₂ Se), krypton (Kr), methyl mercaptan (CH ₃ HS), nitrous oxide (N ₂ O), phosphine ( PH ₃ ), sulfur dioxide (SO ₂ ), sulfur hexafluoride (SF ₆ ), sulfuryl chloride (SO ₂ Cl ₂ ), antimony hydrogen (SbH ₃ ), and xenon (Xe), F-11 (CCl ₃ f) , F-12(CCl ₂ F ₂ ), F-12B1(CClF ₂ Br), F-13B1(CBrF ₃ ), F-20(CHCl ₃ ), F-21(CHCl ₂ F), F-22(CHClF ₂ ), F-30(CH ₂ Cl ₂ ), F-31(CH ₂ ClF), F-32(CH ₂ F ₂ ), F-40(CH ₃ Cl), F-40B1(CH ₃ Br), F-142b(CH ₃ CCIF ₂ ), F-152a(CH ₃ CHF ₂ ), F-12B2(CF ₂ Br ₂ ), F-22B1(CHBrF ₂ ), F-41(CH ₃ F), F-150a (CH ₃ CHCl ₂ ), F-160 (C ₂ H ₆ Cl), F-160B1 (C ₂ H ₅ Br), F-161 (C ₂ H ₅ F) and F-1140 (CH ₂ =CHCl). 24. A method as claimed in claim 6, wherein the step of determining the optimal reduced pressure mass flow rate comprises the substeps of: (a) setting the mass flow rate of the expansion agent at the selected mass flow rate; (b) at approximately the end of the steeping cycle, determine the amount of bulking agent present in the steeped product; (c) adjusting the mass flow rate of the expansion agent by an increment; and (d) Repeat steps (b), (c) and (d) until the maximum amount of bulking agent present in the steeped product is determined.

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